The present invention relates generally to the field of organometallic compounds. In particular, the present invention relates to certain trialkylindium compounds suitable for use in indium vapor deposition processes.
Metal films may be deposited on surfaces, such as non-conductive surfaces, by a variety of means such as chemical vapor deposition (xe2x80x9cCVDxe2x80x9d), physical vapor deposition (xe2x80x9cPVDxe2x80x9d), and other epitaxial techniques such as liquid phase epitaxy (xe2x80x9cLPExe2x80x9d), molecular beam epitaxy (xe2x80x9cMBExe2x80x9d), and chemical beam epitaxy (xe2x80x9cCBExe2x80x9d). Chemical vapor deposition processes, such as metalorganic chemical vapor deposition (xe2x80x9cMOCVDxe2x80x9d), deposit a metal layer by decomposing organometallic precursor compounds at elevated temperatures, i.e., above room temperature, and either at atmospheric pressure or at reduced pressures.
A wide variety of metals may be deposited using such CVD or MOCVD processes. See, for example, Stringfellow, Organometallic Vapor Phase Epitaxy: Theory and Practice, Academic Press, 2nd Edition, 1999, for an overview of such processes. For example, indium is used in a variety of metal films produced by epitaxial growth, particularly in the manufacture of electronic devices such as integrated circuits and light emitting diodes (xe2x80x9cLEDsxe2x80x9d). Exemplary indium containing metal films include indium-phosphide (xe2x80x9cInPxe2x80x9d), indium-gallium-arsenide (xe2x80x9cInGaAsxe2x80x9d), indium-gallium-aluminum-phosphide (xe2x80x9cInGaAIPxe2x80x9d), indium-gallium-arsenic-phosphide (xe2x80x9cInGaAsPxe2x80x9d), indium-gallium-arsenide/gallium-arsenide/aluminum-gallium-arsenide (xe2x80x9cInGaAs/GaAs/AlGaAsxe2x80x9d), indium-arsenide (xe2x80x9cInAsxe2x80x9d), indium-antimonide (xe2x80x9cInSbxe2x80x9d) and indium-arsenic-bismuthide (xe2x80x9cInAsBixe2x80x9d).
Metal layers and alloy layers are typically formed in CVD or MOCVD processes by the decomposition of one or more precursor compounds. A wide variety of precursor compounds may be used. In conventional CVD processes, suitable precursor compounds must have a sufficient vapor pressure to allow them to be transported to the deposition chamber.
Trialkylindium compounds have achieved commercial success as indium sources in vapor phase deposition of indium and indium-containing films. In particular, trimethylindium is the preferred indium source in the formation of indium-phosphide films which are useful in the semiconductor and related electronic industries. Trialkylindium compounds must be highly purified, i.e. substantially free of detectable levels of metallic impurities such as tin, silicon, germanium and zinc, to be useful in such electronic applications. One method for producing highly purified indium source compounds is that disclosed in U.S. Pat. No. 4,847,399 (Hallock et al.). This patent discloses a process for preparing trimethylindium that is very low in metallic impurities, however, such process requires the use of methyl lithium and ether as the reaction solvent. Trace amounts of ether invariably remain associated with the trimethylindium produced by this method.
One of the important uses for trialkylindium compounds, and the primary use for highly purified trialkylindium compounds, is as indium sources for the vapor deposition of indium-containing films in the manufacture of LEDs. Oxygen, if present in any of the metal source compounds, becomes incorporated into the crystal lattice of the film being grown where it contributes excess electrons which can reduce the intensity of light produced by LEDs. Accordingly, trialkylindium compounds having high purity, 5-nines purity with respect to metallic impurities, and extremely low oxygen content are desired.
U.S. Pat. No. 5,756,786 (Power et al.) discloses a process for preparing trimethylindium having high purity without the use of ethereal solvents. This process uses an alkyl exchange reaction between a trihaloindium compound and a trialkylaluminum compound in the presence of a metal fluoride, wherein the molar ratio of the trihaloindium compound to metal fluoride is 1:6. Such a large amount of metal fluoride salt increases the handling and disposal costs of reaction byproducts. In addition, the purification procedure in this patent requires the trimethylindium to be molten, thereby heightening safety and handling concerns.
There is a continuing need for methods of preparing trialkylindium compounds in high yield and purity, while improving the handling and safety associated with such methods and reducing the amount of material for disposal.
It has been surprisingly found that trialkylindium compounds can be prepared using a reduced amount of metal fluoride salt as compared to conventional methods and in a variety of solvents. The present preparation of trialkylindium compounds uses simple purification procedures which avoids molten trialkylindium compounds. In addition, the present invention provides trialkylindium compounds in high yield and high purity.
The present invention provides a method of manufacturing trialkylindium compounds including the steps of: a) reacting a trihaloindium compound with a trialkylaluminum compound in an organic reaction solvent in the presence of a fluoride salt to form a reaction mixture, wherein the molar ratio of the trihaloindium compound to the fluoride salt is at least 1:4.5, and wherein the organic reaction solvent has a boiling point of 100xc2x0 C. or greater; b) separating the organic reaction solvent from the reaction mixture; and c) extracting the trialkylindium compound using an extraction solvent.